The extracellular framework of connective tissues in all metazoan phyla is provided for the most part by a group of structurally related proteins, the collagens. In addition to serving as supportive elements, these macromolecules greatly influence the spatial and ontogenic diversity of extracellular matrices, for they regulate a number of developmental programs and cellular activities, such as adhesion, proliferation and migration. Much information has been accumulated during the past several years on the structure, function and regulation of collagen genes in some vertebrate and invertebrate species. However, given the wide phylogenetic distribution of this gene family, a comprehensive evolutionary picture is still far from being attained. More importantly, the function and regulation of collagen during the crucial stages of early embryonic development has yet to be fully explored. It is the purpose of this application to address these important questions in an organism greatly amenable to the molecular analysis of early developmental processes, the sea urchin embryo. In support of these goals, we have recently isolated and partially characterized genes coding for two echinoid fibrillar procollagen chains. Specifically, we now plan to elucidate the entire structure of the proteins and corresponding genes in order to delineate further the evolution of the deuterostomial collagens. Patterns of collagen expression during embryonic development will be monitored using molecular and immunohistochemical techniques. Transgenic embryos and in vitro assays will be employed to identify sequences responsible for tissue- and stage-specific collagen gene expression, and to characterize their interaction with trans-acting factors. Specific trans-acting factors will be then purified and the cognate genes cloned and characterized. The long term thrust of this work rests on the premise that a better understanding of collagen biology and evolution will shed new light on animal morphogenesis and the relationships between structure and function of proteins.